Copending grandparent application Ser. No. 760,339, the disclosure of which is incorporated herein by reference and made a part hereof, discloses a phase responsive color video signal correction system which allows correction of the spectral distribution and luminance aspects of a phase-encoded composite video signal. U.S. Pat. No. 4,096,523 to Belmares-Sarabia, the disclosure of which is incorporated herein by reference and made a part hereof, discloses another technique for color correcting video signals wherein the primary color video signals are separated into six independent primary and complementary video signals over which separate control can be exercised in making color corrections. The latter system is sometimes known as a "six vector" or "multi-vector" system.
While both of the above-referenced video signal control systems allow color correction of input video signals, both systems leave room for advancement in selecting a portion of an image represented by an input video signal for correction. Most color correction systems are generally hue oriented, in that the controls over video parameters such as hue, saturation, and luminance are grouped or organized according to hue. For example, in the Belmares-Sarabia system a panel of hue, saturation, and luminance controls is provided, there being a separate hue, saturation, and luminance control for each one of the six primary and complementary colors. In the referenced copending phase responsive video signal control system, there is also a separate hue, saturation, and luminance control for each of the color vectors or fans. Both these systems may be considered a "control per hue" system.
While there is a greater selectivity in the phase responsive system which allows an operator to select a hue for correction with greater particularity, the increased number of controls available to the operator which results from greater selectivity sometimes leads to confusion in selection of a color for control. Operators of color correction systems invariably must observe the video scene to be corrected on a color monitor, and observe variations in the image as various controls are moved until the image is aesthetically satisfactory. The proliferation of possible control provided in the control system requires an operator to constantly shift his attention between the image on the video monitor and the control panel to ensure that the proper control is moved and that settings previously made to other portions of the video image are not disturbed. Upon viewing an image which includes a region whose colorimetry is unsatisfactory, the operator must mentally associate the hue of the unsatisfactory region with the set of controls having the most pronounced influence on the region. This leads to possible inefficiencies in operation and slows the color correction process. The more controls there are, i.e. the more hues over which control may be selectively exercised, the more difficult is the task of selecting the proper set.
In U.S. Pat. No. 4,525,736 to Korman, there is shown a device for the modification of the color of television pictures in arbitrarily selected regions of color space and of the picture. This approach relies upon the magnitude of the primary color video signals in order to define a region in color space, as well as the magnitudes of the horizontal and vertical deflection voltages to define a spatial region on the screen for color correction. Signals representing these parameters are provided from a bank of control potentiometers.
The Korman approach does not allow easy identification of either the region in color space for which correction is imposed, or of the region in picture space since no operator feedback is disclosed. Accordingly, the operator must rely upon movement of the control knobs and observe the effects of movement in order to impose a color correction. Needless to say, in a scene by scene color corrector, this requires needless and repetitive movement of the control knobs and necessarily slows down the color correction process.
The Korman patent discloses use of several cathode-ray tube displays to guide the colorist in his choice for the location, shape and size for color modification regions. These allow the colorist to display the original picture, the modified version, the original picture blanked except for the selected region, or the modified version blanked except for the selected region. It would be preferable, however, if an operator of a scene by scene color corrector could view the correction area directly on the scene being color corrected in the context of the scene being corrected, without having to refer to various different displays, or switch between displays, in order to become oriented as to the nature and type of correction being imposed.
Nor does the Korman approach allow multiple simultaneous regions, or one set of corrections for areas inside a selected region and a different set for areas outside the selected region.
In addition, the Korman approach does not allow for the possibility that regions in any given scene selected for color correction may translate or move to a different area of the picture over a series of frames, or the object may be "zoomed in" on or "zoomed out" or may change its orientation as well as position.
Accordingly, there is a need for color video control circuitry which is able to select a portion of a video image for colorimetry correction without requiring an operator to mentally associate a particular hue with a particular set of controls, or to observe a plurality of different monitor scopes in order to define a region for correction. There is also a need for the ability to track a moving selected color correction region over a plurality of frames of a scene by scene color corrector.